1. Field of the Invention
The present invention relates to a drowsiness alarm system and its method of detecting and indicating that the vehicle driver is becoming drowsy on the basis of the pattern of change of a series of steering adjustments when the vehicle is moving at high speed along a road.
2. Description of the Prior Art
Various drowsiness alarm systems for vehicles have been proposed which prevent the vehicle drivers from getting drowsy in order to ensure safe driving.
Japanese Utility Model Registration Publication No. 55-121732 discloses a conventional drowsiness alarm system, the disclosure of which is incorporated by reference, wherein the system recognizes when the vehicle driver becomes drowsy and issues an alarm to the driver when first an episode of no steering adjustments exceeds a predetermined period of time and then a steering adjustment whose speed exceeds a predetermined value over a relatively wide angle of steering occurs. The disclosed system is designed on the basis of the fact that when the driver is drowsy, it is quite likely that there will be no steering adjustments for relatively long periods of time, since the driver would be unresponsive to slight deviations from the desired course, and that such periods of non-steering would be followed by abrupt and wide corrections in the course of travel of the vehicle so that the steering speed over a predetermined angle of steering would be higher than that due to course corrections during normal alert driving.
However, conventional drowsiness alarm systems may produce erroneous alarms depending on road conditions since the reference values used to recognize episodes of non-steering and to determine the steering speed are all fixed. That is to say, for example, in the case when the vehicle travels along a curved road, there is a tendency for a series of abrupt steering adjustments over a wide range of steering angle to occur after a relatively short period of no steering adjustments, and in the case where the vehicle travels along a straight road, there is a tendency for a series of abrupt steering adjustments over a narrow range of steering angle to occur after a relatively longer period of no steering adjustments.
To avoid such erroneous alarms due to the above-described conditions, a reference time used to delimit episodes of no steering adjustments may be extended and a reference time over which the steering speed over a predetermined angle of steering is measured may be shortened. However, if the system were designed as described above, the detection sensitivity would be reduced (it would become difficult to distinguish drowsiness from alertness) and early detection of drowsiness would not be achieved.